import math

x1, y1, x2, y2 = list(map(float, input().split()))
x = x2 - x1
y = y2 - y1
ans = math.sqrt(pow(x, 2) + pow(y, 2))

print(ans)
 import math math x1, y1, x2, y2 = list(map(float, input().split())) x1 list(map(float, input().split())) list map(float, input().split()) map float input().split() ().split () input split y1 x2 y2 x = x2 - x1 x x2 - x1 x2 x1 y = y2 - y1 y y2 - y1 y2 y1 ans = math.sqrt(pow(x, 2) + pow(y, 2)) ans math.sqrt(pow(x, 2) + pow(y, 2)) math.sqrt math sqrt pow(x, 2) + pow(y, 2) pow(x, 2) pow x 2 pow(y, 2) pow y 2 print(ans) print ans y = y2 - y1 y2 - y1 y x1, y1, x2, y2 = list(map(float, input().split())) list(map(float, input().split())) x1 x2, y2 = list(map(float, input().split())) list(map(float, input().split())) x2 y1, x2, y2 = list(map(float, input().split())) list(map(float, input().split())) y1 x = x2 - x1 x2 - x1 x y2 = list(map(float, input().split())) list(map(float, input().split())) y2 ans = math.sqrt(pow(x, 2) + pow(y, 2)) math.sqrt(pow(x, 2) + pow(y, 2)) ans
import math

x1, y1, x2, y2 = list(map(float, input().split()))
x = x2 - x1
y = y2 - y1
ans = math.sqrt(pow(x, 2) + pow(y, 2))

print(ans)

